1. Field of the Invention
The present invention relates to a motor rotation irregularity detection circuit.
2. Description of the Background Art
Conventionally, some motor rotation irregularity detection circuits charge, through a charging circuit, a pulse-width modulation (hereinafter referred to as “PWM”) signal that is generated based on a signal coming from a motor's rotation detector (or magnetic sensor) and in response to the motor's rotation period, and then output an alarm signal indicating rotational irregularities, when the voltage in the charging circuit falls below a reference voltage (c.f., Japanese Patent Application Laid-open No. 9-166610 (Page 2; FIG. 9)).
The aforementioned motor rotation irregularity detection circuits use a PWM signal generated based on a signal coming from the rotation detector provided in the motor. A sensor-less motor with no rotation detector, on the other hand, outputs, in addition to a PWM signal, either a high-level (hereinafter referred to as “H-level”) or low-level (hereinafter referred to as “L-level”) fixed signal, which depends on the timing of such locking when the motor is locked or semi-locked. At this time, with the input of an H-level fixed signal, the voltage in the charging circuit always exceeds a reference voltage, which poses the problem that an alarm signal indicating rotational irregularities may not be output so that irregularities may be assessed as normal.